Intravenous infusion of medication has proved highly effective in treatment of a wide range of clinical conditions, as well as in managing general anaesthesia. Intravenous medications are commonly introduced through an indwelling cannula, most commonly into a peripheral vein, either in combination with a pharmacological acceptable diluent or in alternation therewith. However, the procedure for establishing an intravenous infusion line, more commonly termed an “IV”, can be painful, and is sometimes unsuccessful.
Pain continues to be an important factor in the successful placement of the IV. Not uncommonly, patient discomfort can lead to premature withdrawal of the trocar without first establishing patency of venous placement. Thus there is an unmet need to reduce pain associated with starting an IV.
In order to reduce pain when starting an IV, it has been found that subcutaneous administration of a local anaesthetic in advance of the procedure frequently provides relief. A wheal of lidocaine (2-diethylamino-N-[1,6-dimethylphenyl]acetamide), typically administered as a hydrochloride salt, induces field blockage of pain immediately upon administration. Related local anaesthetics, such as described in Goodman's Pharmacological Basis of Therapeutics, may also be used. It is desirable to administer the minimum amount of these substances as needed to achieve the desired effect.
The local anaesthetic can be administered with a very fine needle, such as a 30 gauge needle, in order to further minimize pain. Needles of this size are typically too small, however, for intravenous therapy. So a separate trocar, more commonly 25 to 16 gauge in size, is used to start the IV. Thus the typical procedure requires two separate devices, the first to administer the local anaesthetic and the second to start the IV, leading to delay and complexity, requiring additional supplies and procedures, and is cumbersome.
Formulation of buffered mixtures is further complicated because the most commonly used local anesthetics are unstable when mixed with a buffer such as sodium bicarbonate, unless used promptly. It is known that delay in usage may lead to weakening of the drug, presumably due to decomposition at neutral or near neutral pH.
Ampoules with breakable necks are also known, and may be used to load a lidocaine:buffer mixture at the point of use. However, breakable ampoules are not uncommonly associated with hand injuries due to sharp edges, and the use of two ampoules to prepare a solution at the bedside is complicated and risks contamination. A frangible seal separating two solutions is described in U.S. Pat. No. 5,261,903 to Dhaliwal, which relates to preparation of buffered anaesthetic solutions for local injection. A displaceable bung is also described in U.S. Pat. No. 3,464,414 to Sponnoble. However, these containers pose unrealistic cost and complexity in modern clinical practice, and do not relieve the need for a first device to administer the anaesthetic followed by a second device to start the IV, both of which must be included in the IV kit and handled separately.
Also of concern is safety for the health practitioner. A device for starting an IV typically includes provision for a retractable hypodermic needle, where the sharp end of the needle is urged inside a housing after activation of a spring mechanism by the user. Surprisingly, while sharps are clearly a factor in transmission of blood borne disease, retractable needles have not been associated with higher safety in cannulation procedures, perhaps because of accidental cuts while operating the mechanism or spatter due to motion of spring-loaded parts. Spring-loaded retractable needles have also been associated with decreased success in pediatric patient populations due to accidental premature retraction of the trocar. Retractable needles are described, for example, in U.S. Pat. Nos. 5,195,985, 5,201,719, 5,885,257, 6,210,371, 6,210,375, and 6368303.
An alternative is an extensible sheath, which may be deployed to advance over the trocar on activation of a spring mechanism by the user, such as is described in U.S. Pat. No. 6,685,676. This mechanism is less likely to be associated with blood splatter but is complex to manufacture and operate.
There is also a need in the art for a convenient single-dose syringe or device permitting point of care administration of a buffered anaesthetic subcutaneously prior to the cannulation. Because it is desirable to prepared the buffered anaesthetic solution immediately before or at the time of use, as shown by Dhaliwal (FIG. 4, U.S. Pat. No. 5,261,903) an improved device or method will supply the anaesthetic and buffer separately in an inexpensive container and is configured to mix the two formulations at the time of injection. Globally the market for intravenous cannulas is estimated to be more than one billion dollars annually. Thus, there is a need in the art for a device and method for starting an IV that overcomes the above disadvantages and has other advantages to improve the process of starting an IV.